Bug Wars

Green Beijing

Kari Heliövaara is the head of forest entomology at the University of Helsinki and the co-author of a standard text, entitled “Insects and Pollution.” A Finn, he has nonetheless spent a good deal of the past decade working in China. “Control strategy”—how to stop insects from killing trees—is one of Heliövaara’s areas of expertise, and he was recently part of a team hired to prevent an ongoing eco-catastrophe from marring the Olympics in Beijing.

For years, a blight had ravaged nearly all the deciduous trees in Beijing, leaving the branches naked and ugly. Civic leaders were worried, in the run-up to the Games, what the bare trees would say about their city’s environmental problems. So, a couple of years ago, they approached the Beijing Forestry University and the Chinese Academy of Forestry and asked if a way could be found to put the leaves back. The Chinese experts—many of whom had worked with or studied under Heliövaara—turned to the Finn for assistance. Heliövaara signed on, and, after he and the scientists discovered that the larvae of moths and sawflies were causing the problem, he helped launch a project called Green Beijing.

“Chemical control was possible but ecologically not recommended,” Heliövaara said the other day. “Precisely planned biological control is much more effective.” Biological control, in this context, means rearing parasites that attack only the defoliating pests. “This is very challenging, and is based on a high level of taxonomic know-how, ” he went on.

He explained how to create an antidote to an infestation: “First, you catch a female moth by net. Second, you catch a male moth using either natural female pheromones or artificial pheromones as a lure. The female moth mates with the male and produces eggs. After a few days, larvae hatch. Then the larvae are infected by parasitic wasps. This is where taxonomic knowledge is crucial. You need to infect the larvae with exactly the correct kind of parasite.”

Heliövaara is, in many respects, a typical Finn, wry and dry and proud. He owns a boat, and, in the summer, sails the Baltic with his family. But nothing excites him as much as talking about insects. “The larval stage takes one month, after which a larva pupates and makes a cocoon,” he continued. “The pupal stage takes another month, and if the larva has been successfully infected, if the female wasp laid her eggs there, only parasites will emerge from the cocoon. The parasites then attack and kill the larvae you’re trying to get rid of.”

Thus, in a mind-boggling and slightly James Bondish fashion, carefully orchestrated insect warfare is set in motion. Over the past decade, Heliövaara and Professor Yang Zhong-qi, of the Chinese Academy of Forestry, have developed this method in a fight against the Siberian moth, which had laid waste to millions of acres of forest in China’s northern provinces. But, given the tight deadline of the Olympics, new laboratories were required for the mass rearing of parasite-infected cocoons.

“They built about twenty huge buildings, in and around Beijing,” Heliövaara said. “Inside each lab are many rearing rooms, and thousands of larvae are feeding in each room simultaneously. Parasites are released into the rooms to lay their eggs in the larvae.”

Last summer, Green Beijing had a successful trial run: leaves returned to deciduous trees in the control area within weeks. So millions more parasite-infected cocoons were prepared, and in May of this year, and again in July, an army of more than a thousand Chinese students, supervised by entomologists, went from tree to tree all over Beijing, putting cocoons on two hundred thousand trees. Each one was attached to the bark by means of a brass screw, the metal piercing only the edge of the cocoon, so that the parasites teeming inside weren’t damaged. Within weeks, about twenty thousand parasites emerged from each cocoon, swarming through the trees and killing the moth and sawfly larvae before the pests could eat up all the foliage.

Heliövaara has been watching the Olympics on television, and he’s pleased with his work. “It is difficult to see the cocoons on the trees,” he said. “But the trees look great on TV. Beijing is green.” ♦

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